This pragma tells the compiler to enable (or disable) the use of POSIX locales for built-in operations (for example, LC_CTYPE for regular expressions, LC_COLLATE for string comparison, and LC_NUMERIC for number formatting). Each "use locale" or "no locale" affects statements to the end of the enclosing BLOCK.

Starting in Perl 5.16, a hybrid mode for this pragma is available,

use locale ':not_characters';

which enables only the portions of locales that don't affect the character set (that is, all except LC_COLLATE and LC_CTYPE). This is useful when mixing Unicode and locales, including UTF-8 locales.